In a semiconductor device manufacturing process, a photoresist is formed on a semiconductor wafer as a target substrate. Then, the photoresist is exposed using a photomask having a predetermined pattern and developed to have the predetermined pattern. By etching the semiconductor wafer by a plasma or the like while using the photoresist as a mask, grooves or holes of various shapes are formed on the semiconductor wafer. Depending on the pattern of the photomask, there may be formed on the semiconductor wafer a region where a density of the patterns of the grooves or the holes is high (hereinafter, referred to as “high-density region”) and a region where a density of the patterns of the grooves or the holes is low (hereinafter, referred to as “low-density region”).
When the high-density region and the low-density region coexist on the semiconductor wafer, there may occur CD (Critical Dimension) loading that is a difference between a dimension of the grooves or the holes formed at the high-density region and a dimension of the grooves or the holes formed at the low-density region. There is known, e.g., a technique for suppressing the occurrence of the CD loading by etching an etching target film by a plasma of a processing gas including an etchant gas comprising halogen species absent fluorine, and an additive gas comprising fluorine species and carbon species (see, e.g., Japanese Patent Application Publication No. 2003-506866)
However, when the pattern formed on the semiconductor wafer has the high-density region and the low-density region, the photoresist used for forming the pattern on the semiconductor wafer also has a high-density region and a low-density region. In the photoresist, a dimension of a mask that defines grooves or holes formed at the low-density region tends to be greater than a dimension of a mask that defines grooves or holes formed at the high-density region. If the dimension of the mask that defines the grooves or the holes formed at the photoresist is different between the high-density region and the low-density region, a dimension of the grooves or the holes formed at a base film that has been etched while using the photoresist film as a mask is also different between the high-density region and the low-density region.